Generally, a process for preparing a semiconductor chip comprises a step of forming fine patterns on a wafer and a step of polishing and packaging the wafer, so as to meet standards of the final device. Said packaging process comprises a step of inspecting a wafer, wherein defectives of semiconductor chips are inspected; a step of dicing, wherein a wafer is cut to separate into each chip; a step of die bonding, wherein the separated chip is attached to a circuit film or a loading plate of a lead frame; a step of wire bonding, wherein circuit pattern of the circuit film or the lead frame is connected to chip pads provided on the semiconductor chip with an electrical connecting means such as a wire; a step of molding, wherein the outside is surrounded with a sealing agent to protect interior circuits of the semiconductor chip and the other parts; a step of trimming, wherein dambar connecting a lead to a lead is cut; a step of forming, wherein the lead is bent into the desired shape; and a step of inspecting a finished product, wherein the finished package is inspected for defective.
In said dicing step, the wafer is cut in a certain thickness using a diamond wheel, and the like. Here, to fix the wafer, a dicing die bonding film is laminated on the back side of the wafer, on which patterns are not formed, under an appropriate temperature condition.
Generally, as shown in FIG. 2, a dicing die bonding film consists of a dicing film and a die bonding film, which is attached to the back side of wafer that patterns are not formed. In a dicing process, the whole wafer and a part of the base films of the die bonding film is cut, using a diamond wheel (blade).
In such a dicing process, a wafer is damaged by applying excessive pressure or mechanical impact thereto, and chippings are generated, thereby causing to frequently generate burrs which may contaminate patterns. In addition, while the thickness of wafer is thinned as the packaging has a small size and the dicing conditions become severe for increase of production efficiency, said problems frequently happen. Especially, while the thickness of wafer decreases, there are many cases in which even burrs having a length in a level without any problem formerly, climb onto a die, and they cause defectives.
A component of burrs climbing onto the die is principally a die bonding film. The reason is as follows. A pressure sensitive adhesive part of a dicing film is coated on a base film and well adhered thereto, so that in dicing, there are few cases in which burrs climb onto the die, even though burrs are caused by the pressure sensitive adhesive part and the base film. But, the die bonding film is mechanically laminated with the pressure sensitive adhesive part of the dicing film via a tailoring process and completely cut. Therefore, its adhesion strength is relatively lowered, so that incidence of burrs to climb onto the die increases. To solve this problem, it is important to increase adhesion of the pressure sensitive adhesive part of the dicing film to the die bonding film, and of the wafer to the die bonding film. However, when an adhesive film has high adhesion strength to increase the adhesion, it has a low elasticity, so that the burr amount increases by elongation of the die bonding film itself. When the die bonding film has too high elasticity, it has low adhesion strength, so that on dicing, shaking increases and the burr incidence rises. Therefore, it is a major factor, for lowering the burr incidence, to control the elasticity of the adhesive film.
In Japanese Unexamined Patent Publication No. 2005-330300, an adhesive resin composition having a tensile elasticity of 0.5 MPa or less at 100° C. or less before thermosetting, of 0.2 MPa or more at 180° C., and of 1 MPa to 10 MPa at 260° C. after thermosetting is disclosed. However, considering the dicing process to generate heat at a moment, it has a limit in expecting characteristics of a film, to measure elasticity in a condition that heat is sufficiently applied to a specimen with a certain speed of elevating temperature. In addition, it was confirmed as research results of the present invention that the burr incidence depends on thickness, despite of the same composition and elasticity, and it had hard to control burrs by conventional measurements of elasticity.
Therefore, a novel method is required, which may predict and control burr incidence in the die bonding film, and thus, it needs to provide a semiconductor device having excellent workability and reliability.